Esophagitis found upon endoscopy is an objective indication of the likely presence of reflux, but endoscopy is not routinely performed in all centers that have reported their series. Stratification of severity in esophagitis is mostly reported using the Los Angeles classification of esophagitis [12].

Rate of esophagitis seen upon endoscopy had a larger variation compared with rate of symptoms, ranging from 6.3 to 64.7% (Table 13.2). The proportion of studied patients who received an endoscopy also varies quite significantly from 10 to 100%. Series with a lower endoscopy surveillance rate often report a higher incidence of esophagitis, likely due to selection bias. Studies with less than 60% of the studied patients having had endoscopy all reported an incidence of over 50% [4, 8, 13]. The incidence in the remaining reports still varies significantly, but most reports lie within 20–42%.

As in primary GERD, discordance between the rates of reflux symptoms and endoscopic evidence of reflux disease exists. Presence of symptoms has low sensitivity in predicting the presence of mucosal damage. As many as 88.9% of patients with esophagitis of Los Angeles Classification grade A or above can be asymptomatic, as reported by Shiwaku et al. [14] Some groups also reported a rate of 10% to almost 70% of asymptomatic patients having esophagitis (Table 13.2). Since long-standing esophagitis left untreated may lead to severe consequences, many authors advocate regular endoscopic surveillance to facilitate timely intervention.

Gastroesophageal reflux disease can also be objectively diagnosed using pH studies. Overall, the rate of an abnormal pH study generally ranges from 20.2% [15] to 57.7% [16], excluding one series in which pH testing was only provided for a single patient who had reflux symptoms registering 13.4% total time with esophageal acid exposure [17]. Assessing reflux with pH testing provides reliable objective data; however, diagnosing GERD with such a singular test may also lack standardization with the presence of different measurement methods and parameters.

In the literature, both 24-h probe-based monitoring and more prolonged monitoring using wireless capsules are used in different centers, some even within the same center (Table 13.3). Prolonged pH studies with wireless capsules are shown to be more sensitive in detecting pathological esophageal acid exposure and positive symptom association [18, 19]. Different normative values of percentage of total time of abnormal esophageal acid exposure for the wireless capsule system, ranging from 4.4 to 5.3%, have been reported [19, 20], which are slightly higher than the most referenced 4.2% for probe-based monitoring [21].